EE380: Computer Systems Colloquium Seminar Optional Static Typing for Python Speaker: Guido van Rossum, Dropbox & Python Software Foundation Python is a dynamically typed language, and some of its appeal derives from this. Nevertheless, especially for large code bases, it would be nice if a compiler could find type errors before the code is even run. Optional static type checking promises exactly this, and over the past four years we have successfully introduced this feature into Python 3. This talk introduces the type system we've adopted and the syntax used for type annotations, some tips on how to get started with a large existing code base, and our experience using the 'mypy' type checker at Dropbox. The entire system is open source, and has also been adopted by other companies such as Lyft, Quora and Facebook. About the Speaker: Guido van Rossum is the creator of Python. Born in the Netherlands, he moved to the US following Python's success. He has worked at various startups and Google, and is currently a Principal Engineer at Dropbox. For more information about this seminar and its speaker, you can visit https://ee380.stanford.edu/Abstracts/180606.html Support for the Stanford Colloquium on Computer Systems Seminar Series provided by the Stanford Computer Forum. Colloquium on Computer Systems Seminar Series (EE380) presents the current research in design, implementation, analysis, and use of computer systems. Topics range from integrated circuits to operating systems and programming languages. It is free and open to the public, with new lectures each week. Learn more: http://bit.ly/WinYX5 0:00 Introduction 0:33 Python's popularity 3:24 Python's type system 10:31 Why dynamic typing 11:42 Why static typing 13:26 Gradual typing 17:30 The mypy project 22:24 Other static type checkers for Python 23:46 A static type system for Python 27:51 Example in Python 2 28:55 Type inference 31:42 How to spell types 36:40 Escape hooks (unsafe) 39:44 Generics 40:55 Generic class example 43:36 Analyzing runtime type checks 48:03 Protocols (PEP 544) (2) 54:05 Stub files and typeshed 55:34 How to start on a large code base 59:06 Standardization effort